WO1992008465A2

WO1992008465A2 - 2-decarboxyl-2-aminoalkyl-prostaglandins as ocular hypotensives

Info

Publication number: WO1992008465A2
Application number: PCT/US1991/007982
Authority: WO
Inventors: Ming Fai Chan; David Frederick Woodward
Original assignee: Allergan, Inc.
Priority date: 1990-11-09
Filing date: 1991-10-30
Publication date: 1992-05-29
Also published as: WO1992008465A3; NZ240502A; US5270049A; EP0556296B1; AU656752B2; IE913906A1; HU9301327D0; HUT70500A; IL99975A0; DE69127755D1; ZA918869B; JPH06501482A; AU9041491A; EP0556296A1; CA2095430A1; JP3488456B2; ES2107522T3; ATE158506T1; DE69127755T2; IL99975A

Abstract

The present invention concerns 2-decarboxyl-2-aminoalkyl derivatives of naturally occurring and synthetic prostaglandins, N-substituted derivatives, ester prodrugs and homologues of such compounds that are potent ocular hypotensives, and are particularly suitable for the management of glaucoma.

Description

2-DECARTOXYL-2-AMINOALKYL-PROSTAGLANDINS AS

OCULAR HYPOTENSTVES

Field of the Invention

The present invention relates to 2-decarboxyl-2-aminoalkyl prostaglandin derivatives. More particularly, the present invention concerns 2-decarboxyl-2-aminoalkyl derivatives of naturally occurring and synthetic prostaglandins, N-substituted derivatives, ester prodrugs and homologues of such compounds that are potent ocular hypotensives, and are particularly suitable for the management of glaucoma.

Background of the Invention

Ocular hypotensive agents are useful in the treatment of a number of various ocular hypertensive conditions, such as post-surgical and post-laser trabeculectomy ocular hypertensive episodes, glaucoma, and as presurgical adjuncts.

Glaucoma is a disease of the eye characterized by increased intraocular pressure. On the basis of its etiology, glaucoma has been classified as primary or secondary. For example, primary glaucoma in adults (congenital glaucoma) may be either open-angle or acute or chronic angle-closure. Secondary glaucoma results from pre-existing ocular diseases such as uveitis, intraocular tumor or an enlarged cataract.

The underlying causes of primary glaucoma are not yet known. The increased intraocular tension is due to the obstruction of aqueous humor outflow. In chronic open-angle glaucoma, the anterior chamber and its anatomic structures appear normal, but drainage of the aqueous humor is impeded. In acute or chronic angle-closure angle-closure glaucoma, the anterior chamber is shallow, the filtration angle is narrowed, and the iris may obstruct the trabecular meshwork at the entrance of the canal of Schlemm. Dilation of the pupil may push the root of the iris forward against the angle, and nay produce pupillary block and thus precipitate an acute attack. Eyes with narrow anterior chamber angles are predisposed to acute angle-closure glaucoma attacks of various degrees of severity.

Secondary glaucoma is caused by any interference with the flow of aqueous humor from the posterior chamber into the anterior chamber and subsequently, into the canal of Schlemm. Inflammatory disease of the anterior segment may prevent aqueous escape by causing complete posterior synechia in iris bombe, and may plug the drainage channel with exudates. Other common causes are intraocular tumors, enlarged cataracts, central retinal vein occlusion, trauma to the eye, operative procedures and intraocular hemorrhage.

Considering all types together, glaucoma occurs in about 2% of all persons over the age of 40 and may be asymptotic for years before progressing to rapid loss of vision. In cases where surgery is not indicated, topical β-adrenoreceptor antagonists have traditionally been the drugs of choice for treating glaucoma.

Certain eicosanoids and their derivatives have been reported to possess ocular hypotensive activity, and have been recommended for use in glaucoma management. Eicosanoids and derivatives include numerous biologically important compounds such as prostaglandins and their derivatives. Prostaglandins can be described as derivatives of prostanoic acid which has the following structural formula: Various types of prostaglandins are known, depending on the structure and substituents carried on the alicyclic ring of the prostanoic acid skeleton. Further classification is based on the number of unsaturated bonds in the side chain indicated by numerical subscripts after the generic type of prostaglandin [e.g. prostaglandin E₁ (PGE₁), prostaglandin E₂ (PGE₂)], and on the configuration of the substituents on the alicyclic ring indicated by α or β [e.g. prostaglandin F_2α (PGF_2α)].

Prostaglandins were earlier regarded as potent ocular hypertensives, however, evidence accumulated in the last decade shows that some protaglandins are highly effective ocular hypotensive agents, and are ideally suited for the long-term medical management of glaucoma (see, for example, Bito, L. Z. Biological Protection With Prostaglandins

Cohen, M. M., ed., Boca Raton, Fla, CRC Press Inc., 1985, pp. 231-252; and Bito, L. Z., Applied Pharmacology in the Medical Treatment of Glaucomas Drance, S. M. and Neufeld, A. H. eds., New York, Grune & Stratton, 1984, pp. 477-505). Such prostaglandins include PGF_2α, PSF_1α, PGE₂, and certain lipid-soluble esters, such as C₁ to C₂ alkyl esters, e.g. 1-isopropyl ester, of such compounds.

Although the precise mechanism is not yet known, recent experimental results indicate that the prostaglandin-induced reduction in intraocular pressure results from increased uveoscleral outflow [Nilsson et al., Invest. Qphthalmol. Vis. Sci. 28(suppl). 284 (1987)].

The isopropyl ester of PGF_2α has been shown to have significantly greater hypotensive potency than the parent compound, presumably as a result of its more effective penetration through the cornea. In 1987 this compound was described as "the most potent ocular hypotensive agent ever reported" [see, for example, Bito, L. Z., Arch. Ophthalmol. 105, 1036 (1987), and Siebold et al., Prodrug 5, 3 (1989)]. Whereas prostaglandins appear to be devoid of significant intraocular side effects, ocular surface

(conjunctival) hyperemia and foreign-body sensation have been consistently associated with the topical ocular use of such compounds, in particular PGF_2α and its prodrugs, e.g. its 1-isopropyl ester, in humans. The clinical potentials of prostaglandins in the management of conditions associated with increased ocular pressure, e.g. glaucoma are greatly limited by these side effects.

In a series of co-pending United States patent applications assigned to Allergan, Inc. prostaglandin esters with increased ocular hypotensive activity accompanied with no or substantially reduced side-effects are disclosed. The co-pending USSN 386,835 (filed 27 July 1989), relates to certain 11-acyl-prostaglandins, such as

11-pivaloyl, 11-acetyl, 11-isobutyryl, 11-valeryl, and 11- isovaleryl PGF_2α. Intraocular pressure reducing 15-acyl prostaglandins are disclosed in the co-pending application

USSN 357,394 (filed 25 May 1989). Similarly, 11,15- 9,15- and 9,11-diesters of prostaglandins, for example 11,15- dipivaloyl PGF_2α are known to have ocular hypotensive activity. See the co-pending patent applications USSN Nos.

385,645, 386,312 and 386,834 (all filed 27 July 1989). PGF

1-alcohols and their use as ocular hypotensives are disclosed in co-pending patent application USSN

(filed 14 June 1990). The disclosures of all of these patent applications are hereby expressly incorporated by reference.

Certain 2-decarboxyl-2-aminomethyl PG derivatives are known in the art.

N-dimethylamino-2-decarboxy PGF_2α was, for example, described by Fitzpatrick et al., in NATO Adv. Study Inst.

Ser., Ser. A, A36, 283-289 (1981). The compound attenuated

PGF_2α-induced increases in lobular arterial pressure of perfused canine lung in situ. 2-decarboxyl-2-aminomethyl PGF_2α-type analogues were disclosed by Nelson et al., in Prostaglandins 17(3), 441-449 (1979). According to this publication, the disclosed analogues closely resemble the parent PGF_2α compounds as antifertility agents in the hamster.

2-decarboxyl-2-aminomethyl-5,9-alpha-prostacyclin analogues, especially of the F series, are disclosed in the Belgian Patent Application No. 860,278, claiming the priority Of USSN 788,143, filed 19 April 1977.

Maddox et al., Nature 273, 549-552 (1978) tested the antagonistic behaviour of fourteen amide and 1-amino derivatives of prostaglandin F compounds, using the response of gerbil colon to PGF_2α.

2-decarboxyl-2-aminomethyl PGE nd PGD analogues are disclosed in the United States Patent No. 4,085,139.

There is no mention in any of the foregoing publications of the ocular hypotensive activity of 1-decarboxy-1-aminomethyl prostaglandin derivatives.

Summary of the Invention

We have surprisingly found that 2-decarboxyl-2-aminomethyl derivatives of prostaglandins are distinctly more potent than their parent compounds. Also, especially in lower doses, they cause significantly lower ocular surface hyperemia than the parent compounds.

Accordingly, the present invention concerns a method of treating ocular hypertension which comprises applying to the eye an amount sufficient to treat ocular hypertension of a compound of formula (I)

wherein the wavy line attachments indicate either alpha (α) or beta (β) configuration; hatched lines indicate α configuration, solid triangles are used to indicate β configuration; the dashed bonds represent a single bond or a double bond which can be in the cis or trans configuration; R₁ and R₂ independently are hydrogen, an aliphatic hydrocarbon group having from 1 to about 6 carbon atoms, or a -CO(Y) group, wherein Y is an aliphatic hydrocarbon group having from 1 to about 6 carbon atoms; R₃ and R₄ independently are hydrogen, or an aliphatic hydrocarbon group having from 1 to about 6 carbon atoms; one of R₅ and R₆ is =O, -OH or an -O(CO)R₈ group, and the other one is -OH or an -O(CO)R₈ group or R₅ is =0 and R₆ is

H; R₇ is -OH or -O(CO)R₈, wherein R₈ is a saturated or unsaturated acyclic hydrocarbon group having from 1 to about 20 carbon atoms, or -(CH₂)_nR₉ wherein n is 0-10, and

R₉ is an aliphatic ring from about 3 to about 7 carbon atoms, or an aromatic or heteroaromatic ring; or a pharmaceutically acceptable salt thereof.

In a further aspect, the present invention relates to an ophthalmic solution comprising a therapeutically effective amount of a compound of formula (I), wherein the symbols have the above meanings, or a pharmaceutically acceptable salt thereof, in admixture with a non-toxic, ophthalmically acceptable liquid vehicle, packaged in a container suitable for metered application.

In a still further aspect, the present invention relates to a pharmaceutical product, comprising

a container adapted to dispense its contents in metered form; and

an ophthalmic solution therein, as hereinabove defined.

Detailed Description of the Invention The present invention relates to the use of 2- decarboxyl-2-aminoalkyl prostaglandin compounds, and their derivatives and analogues as ocular hypotensives. The prostaglandin derivatives used in accordance with the present invention are encompassed by the structural formula (I)

wherein the substituents and symbols are as hereinabove defined.

The above formula includes 2-decarboxyl-2-aminoalkyl derivatives of prostaglandins of the F, D, E, A and B series. A preferred group of the compounds of the present invention is encompassed by the following formula (II)

wherein R₅/R₆ is -OH/-OH, =O/-OH, -OH/=O and the esters of these compounds. This definition includes PGF, PGE, and PGD derivatives.

Particularly preferred are the PGF_2α derivatives of the formula (III)

and their 9- and/or 11- and/or 15-esters . In all of the above formulae, as well as in those provided hereinafter, the dotted lines on bonds between carbons 5 and 6 (C-5), between carbons 13 and 14 (C-13), between carbons 8 and 12 (C-8), between carbons 10 and 11 (C-10) and between carbons 17 and 18 (C-17) indicate a single or a double bond which can be in the cis or trans configuration. If two solid lines are used that indicates a specific configuration for that double bond. Hatched lines at positions C-9, C-11 and C-15 indicate the α configuration. If one were to draw the β configuration, a solid triangular line would be used.

The naturally occurring stereochemistry of PGF_2α includes the C-9, C-11, and C-15 hydroxyl groups in the α configuration. In the compounds used in accorance with the present invention, however, prostaglandins having the C-9 or C-11 or C-15 substituents in β configuration are also contemplated. As hereinabove mentioned, in all formulas provided herein broken line attachments to the cyclopentane ring indicate substituents in the α configuration. Thickened solid line attachments to the cyclopentane ring indicate substituents in the β configuration. For instance, 9β-PGF compounds have the same structure as PGF_α compounds, except that the hydroxyl at the C-9 position is in the β configuration. Also, the broken line attachment of the hydroxyl group or other substituent to the C-11 and

C-15 carbon atoms signifies the a. configuration; therefore, compounds with the epi configuration for the hydroxyl group at C-15 are designated by using 150 and if there is no indication of the β configuration, the configuration is assumed α .

In the substituent definitions, the "aliphatic hydrocarbon groups" have from 1 to about 6, most preferably 1 to about 4 carbon atoms. The aliphatic hydrocarbon groups may be straight or branched chained, saturated or unsaturated, such as straight or branched chained alkyl, alkenyl, alkynyl groups. Typical representatives of the alkyl groups include, for example, methyl, ethyl, n- and isopropyl, n-, sec-, iso- and tert-butyl, n- and isopentyl, n- and neohexyl, etc. groups. Typical alkenyl and alkynyl groups are vinyl, allyl, propenyl, ethynyl and propargyl.

The definition of R₈ may include a cyclic component, -(CH₂)_nR₉, wherein n is 0-10, R₉ is an aliphatic ring from about 3 to about 7 carbon atoms, or an aromatic or heteroaromatic ring. The "aliphatic ring" may be saturated or unsaturated, and preferably is a saturated ring having 3-7 carbon atoms, inclusive. As an aromatic ring, R₉ preferably is phenyl, and the heteroaromatic rings have oxygen, nitrogen or sulfur as a heteroatom. Preferably n is 0-4.

The most preferred compounds are those PGF_2α derivatives in which both R₁ and R₂ are hydrogen or one of R₁ and R₂ is hydrogen, and the other one is an aliphatic hydrocarbon group having from 1 to 6, preferably 1 to 4 carbon atoms. Particularly preferred are the compounds in which R₃ and R₄ both represent hydrogen.

Especially preferred compounds of formula (I) are:

2-decarboxyl-2-dimethylaminomethyl PGF_2α, and

2-decarboxyl-2-aminomethyl PGF_2α.

The compounds of the present invention can be prepared by methods known in the art. A typical synthesis route is illustrated in Reaction Scheme I, wherein step a) is typically performed with CH₂N₂ in ethanol/methanol; in step b) a suitable amine or its hydrochloride is used as reactant, and the reaction is performed in a sealed tube, at about 70ºC; and step c) is accomplished in excess LiAlH₄/THF, at about 25ºC.

A pharmaceutically acceptable salt is any salt which retains the activity of the parent compound and does not impart any deleterious or undesirable effect on the subject to whom it is administered and in the context in which it is administered . Of particular interest are the acid addition salts of the amine compounds of the present invention.

Pharmaceutical compositions may be prepared by combining a therapeutically effective amount of at least one compound according to the present invention, or a pharmaceutically acceptable salt thereof, as an active ingredient, with conventional ophthalmically acceptable pharmaceutical excipients, and by preparation of unit dosage forms suitable for topical ocular use. The therapeutically efficient amount typically is between about 0.0001 and about 5% (w/v), preferably about 0.001 to about 1.0% (w/v) in liquid formulations.

For ophthalmic application, preferably solutions are prepared using a physiological saline solution as a major vehicle. The pH of such ophthalmic solutions should preferably be maintained between 6.5 and 7.2 with an appropriate buffer system. The formulations may also contain conventional, pharmaceutically acceptable preservatives, stabilizers and surfactants.

Preferred preservatives that may be used in the pharmaceutical compositions of the present invention include, but are not limited to, benzalkonium chloride, chlorobutanol, thimerosal, phenylmercuric acetate and phenylmercuric nitrate. A preferred surfactant is, for example, Tween 80. Likewise, various preferred vehicles may be used in the ophthalmic preparations of the present invention. These vehicles include, but are not limited to, polyvinyl alcohol, povidone, hydroxypropyl methyl cellulose, poloxamers, carboxymethyl cellulose, hydroxyethyl cellulose and purified water.

Tonicity adjustors may be added as needed- or convenient. They include, but are not limited to, salts, particularly sodium chloride, potassium chloride, mannitol and glycerin, or any other suitable opthalmically acceptable tonicity adjustor. Various buffers and means for adjusting pH may be used so long as the resulting preparation is ophthalmically acceptable. Accordingly, buffers include acetate buffers, citrate buffers, phosphate buffers and borate buffers. Acids or bases may be used to adjust the pH of these formulations as needed.

In a similar vein, an ophthalmically acceptable antioxidant for use in the present invention includes, but is not limited to, sodium metabisulfite, sodium thiosulfate, acetylcysteine, butylated hydroxyanisole and butylated hydroxytoluene.

Other excipient components which may be included in the ophthalmic preparations are chelating agents. The preferred chelating agent is edentate disodium, although other chelating agents may also be used in place or in conjunction with it.

The ingredients are usually used in the following amounts:

Ingredient Amount (% w/v)

active ingredient about 0.001-5

preservative 0-0.10

vehicle 0-40

tonicity adjustor 1-10

buffer 0.01-10

pH adjustor q.s. pH 4.5-7.5

antioxidant as needed

surfactant as needed

purified water as needed to make 100%

The actual dose of the active compounds of the present invention depends on the specific compound, and on the condition to be treated; the selection of the appropriate dose is well within the knowledge of the skilled artisan.

The ophthalmic formulations of the present invention are conveniently packaged in forms suitable for metered application, such as in containers equipped with a dropper, to facilitate the application to the eye. Containers suitable for dropwise application are usually made of suitable inert, non-toxic plastic material, and generally contain between about 0.5 and about 15 ml solution.

The invention is further illustrated by the following non-limiting Examples.

Example 1

2-Decarboxyl-2-dimethylaminomethyl PGF_2α

PGF_2α methyl ester (47.6 mg, 0.129 mmol) was placed in a pressure flask. About 2 al of dimethylamine was condensed into the flask by using a dry ice-acetone bath and dimethylamine hydrochloride (78 mg) was added. The flask was sealed and heated at 75ºC for 44 h. The flask was cooled to -78ºC and opened. Excess dimethylamine was swept away by a stream of argon at 25ºC. The residue was partitioned between saturated ammonium chloride and ethyl acetate. After extracting with ethyl acetate, the organic layer was washed with water and brine and dried over magnesium sulfate. Removal of solvent gave an oil which was purified by means of flash chromatography on silica gel using 14:1 methylene chloride/methanol as eluent to give

38 mg pure PGF_2α dimethylamide. IR: 1630 cm^-1.

To a solution of PGF_2α dimethylamide (27 mg,

0.07 mmol) in anhydrous tetrahydrofuran (1.0 ml) was added a solution of lithium aluminum hydride (1.0 M, 0.28 ml,

0.28 mmol) at 0ºC. The solution was allowed to warm up to room temperature and stirred for 18 h. The reaction was quenched with a few drops of methanol and concentrated under vacuum. The residue was taken up in ethyl acetate (5 ml), washed with water and brine and dried over magnesium sulfate. Evaporation of solvent gave a crude product which was purified by preparative thin layer chromatography (silica gel plates, ammonia saturated methanol/metehylene chloride 1:9) to give 8.5 mg of 2-decarboxyl-2-dimethylaminomethyl PGF_2α. ¹H NMR (300 MHz, CDCI₃): δ5.53 (2H, ABX, J_AB=15.3, J_AX=6, J_BX=7.3Hz) , 538 (2H, complex AB), 4.16 (1H, t, J=3.9 Hz), 4.06 (1H, q, J=6.2 Hz), 3.96 (1H, m), 1.7-2.4 (12H, m) , 2.21 (6H, s), 1.79 (1H, br d, J-15 Hz), 1.2-1.65 (12H, m), 0.88 PPM (3H, t, J=6.7 Hz); ¹³C NMR (75 MHz, CDCI₃): 5135.30, 132.75, 130.78, 128.77, 78.18, 72.86, 72.60, 59.18, 55.84, 50.59, 45.10, 42.94, 37.14, 31.58, 26.88, 26.69, 26.59, 25.30, 25.05, 22.41, 13.80 ppm;

MS (Cl): m/z 584 (M+, 100%), 512 (8%), 90 (20%) ;

HRMS: calculated for C₃₁H₆₆O₃NSI_O:584.4351, found: 584.4343.

Example 2

2-Decarboxyl-2-aminomethyl PGF_2α

In a similar manner, 2-decarboxyl-2-aminomethyl PGF_2α was prepared from PGF_2α, ammonia and ammonium chloride.

¹H NMR (300 MHz, CDCI₃): 55.48 (2H, ABX, J_AB=15,

J_AX=6, J_BX=8 Hz), 5.27-5.4 (2H, m), 4.10 (1H, t, J=4 Hz),

4.02 (1H, q, J=6 Hz), 3.91 (1H, m), 3.2-3.4 (5H, br s),

2.71 (2H, t, J=7 Hz, CH₂-NH₂), 1.2-2.4 (20H, m), 0.84 ppm (3h, distorted t, J-6Hz) ;

¹³C NMR (75 M Hz, CDCI₃) : δ 135.60, 132.77, 130.46, 128.90, 77.84, 72.80, 72.46, 55.68, 50.40, 42.96, 40.71, 37.12, 31.60, 30.90, 26.39, 26.16, 25.27, 25.08, 22.43, 13.81 ppm;

MS (Cl, NH₃, TMS derivative) : m/z 628 (M+1, 100%) , 200

(16), 145 (22), 90 (77) ;

HRMS (Cl, TMS derivative) : calculated for C₃₂H₇₀O₃NSi₄: 628.4433, found 628.4413. Example 3

Intraocular Pressure Reducing Activity

Experimental quantities of the test compounds were prepared in an ophthalmic formulation containing 0.1% polysorbate (Tween 80) - 10mM TRIS. One eye of each experimental animal was treated by applying one 25 μl drop of the drug formulation to the ocular surface, the contralateral eye received 25 μl of vehicle as a control. Intraocular pressure was measured by applanation pneumatonometry immediately before drug administration and at subsequent, predetermined times thereafter. New Zealand albiio/dutch belted cross rabbits were employed as experimental animals.

Ocular surface hyperemia was assessed by observation at predetermined times after drug administration and is described as either present or absent.

The data obtained are shown in Tables 1 and 2.

The foregoing description details specific methods and compositions that can be employed to practice the present invention, and represents the best mode conteaplated. However, it is apparent from one of ordinary skill in the art that further compounds with the desired pharmacological properties can be prepared in an analogous Banner, and that the disclosed compounds can also be obtained from different starting compounds via different chemical reactions. Similarly, different pharmaceutical compositions may be prepared and used with substantially the same results. Thus, however detailed the foregoing may appear in text, it should not be construed as limiting the overall scope hereof; rather, the ambit of the present invention is to be governed only by the lawful construction of the appended claims.

Claims

Claims:

1. A method of treating ocular hypertension which comprises applying to the eye an amount sufficient to treat ocular hypertension of a compound of formula (I)

wherein the wavy line attachments indicate either alpha (α) or beta (β ) configuration; hatched lines indicate α configuration, solid triangles are used to indicate β configuration; the dashed bonds represent a single bond or a double bond which can be in the cis or trans configuration; R ₁ and R₂ independently are hydrogen, an aliphatic hydrocarbon group having from l to about 6 carbon atoms, or a -CO(Y) group, wherein Y is an aliphatic hydrocarbon group having from 1 to about 6 carbon atoms; R₃ and R₄ independently are hydrogen, or an aliphatic hydrocarbon group having from 1 to about 6 carbon atoms; one of R5 and R₆ is =O, -OH or an -O(CO)R₈ group, and the other one is -OH or an -O(CO)R₈ group or R₅ is =0 and R₆ is H; R₇ is -OH or -O(CO)R₈, wherein R₈ is a saturated or unsaturated acyclic hydrocarbon group having from 1 to about 20 carbon atoms, or -(CH₂)_nR₉ wherein n is 0-10, and R₉ is an aliphatic ring from about 3 to about 7 carbon atoms, or an aromatic or heteroaromatic ring; or a pharmaceutically acceptable salt thereof.

2. The method of Claim l wherein said compound of formula (I) is selected from the group consisting of naturally occurring prostaglandins of the D, E and F series.

3. The method of Claim 1 wherein said compound is a PG derivative of the formula (II)

wherein R₁, R₂, R₃ and R₄ are as defined in Claim 1 and R₅/R₆ is -OH/-OH, =O/-OH, -OH/=O, or an -O(CO)R₈ ester thereof.

4. The method of Claim 3 wherein said compound is a PGF_2α derivative of the formula (III)

wherein R₁, R₂, R₃ and R₄ are as defined in Claim 1.

5. The method of Claim 4 wherein in the formula both R₁ and R₂ are hydrogen or one of R₁ and R₂ is hydrogen, and the other one is an aliphatic hydrocarbon group having from 1 to 6 carbon atoms, and R₃ and R₄ are as defined in Claim 1.

6. The method of Claim 5, wherein in the formula R₃ and R₄ both are hydrogen.

7. The method of Claim 6 wherein said compound of formula (I) is selected from the group consisting of

2-decarboxyl-2-aminomethyl PGF_2α, and

2-decarboxyl-2-dimethylaminomethyl PGF_2α.

8. An ophthalmic solution comprising a therapeutically effective amount of a compound of formula (I), as defined in Claim 1, or a pharmaceutically acceptable salt thereof, in admixture with a non-toxic, ophthalmically acceptable liquid vehicle, packaged in a container suitable for metered application.

9. A pharmaceutical product, comprising

a container adapted to dispense the contents of said container in metered form; and

an ophthalmic solution in said container comprising a compound of formula (I) as defined in Claim 1, or a pharmaceutically acceptable salt thereof, in admixture with a non-toxic, ophthalmically acceptable liquid vehicle.